Conventionally, an electrically heated catalyst (EHC) is known as an exhaust air purification device that is arranged on an exhaust path of a car and the like having an engine and that purifies an exhaust gas from the engine (for example, see JP 3334897 B2).
As shown in FIG. 10, an exhaust air purification device 100 as a conventional EHC has a hollow case 110 as an exterior thereof, a cylindrical carrier 120 having honeycomb structure that is housed in the case 110 and that has a catalyst such as platinum and palladium supported thereon, electrodes 130, 140 arranged on the outer circumferential surface of the carrier 120 so as to oppose each other and connected electrically to the carrier 120, and terminals 150, 160 connected electrically to the electrodes 130, 140, respectively and connected electrically to a power source such as a battery through wire harnesses and the like. The exhaust air purification device 100 heats the carrier 120 electrically with an electric current supplied from the power source and flowing between the electrodes 130, 140 so that the catalyst supported on the carrier 120 is heated to an active temperature thereof, and purifies toxic substances such as unburned hydrocarbon (HC), carbon monoxide (CO) and nitrogen oxide (NOx) contained in the exhaust gas from the engine by the catalytic reaction.
As mentioned above, the catalyst supported on the carrier 120 can purify the exhaust gas by the catalytic reaction in the case where a temperature thereof reaches the active temperature. However, in the case where a temperature of the catalyst does not reach the active temperature when the engine is started, especially when the engine is run in a cold-start mode, the problem occurs that the toxic substances contained in the exhaust gas are not purified and exhausted to the atmosphere.
In the exhaust air purification device 100, an electric current that flows in the carrier 120 through the electrodes 130, 140 flows through a part with low resistance in the carrier 120 preferentially. Therefore, the carrier 120 may not be uniformly heated, and there may be a part of the catalyst supported on the carrier 120 whose temperature does not reach the active temperature when the engine is run in a cold-start mode, so that the toxic substances contained in the exhaust gas are not purified enough. If the carrier 120 is heated to reach the active temperature in the whole part of the catalyst, power consumption unfortunately increases.
Moreover, in the exhaust air purification device 100, the electrodes 130, 140 are arranged on the outer circumferential surface of the carrier 120 so as to oppose each other with the phase difference of 180 degrees. Therefore, the terminals 150, 160 are arranged in the range where the electrodes 130, 140 on the outer circumferential surface of the carrier 120 are arranged. Namely, the terminals 150, 160 are arranged each other with the phase difference of approximately 180 degrees. The terminals 150, 160 are opposed to each other on the outer circumferential surface of the carrier 120, so that, for example, in the case where the exhaust air purification device 100 is installed under the floor of a car, it is necessary to secure a large space under the floor. Consequently, that is disadvantage in that an interior space of the car must be reduced.
[Patent Literature 1] JP 3334897 B2